1. Field of the Invention
The present invention relates to an apparatus for producing hydrogen by a steam reforming reaction using a hydrocarbon or an oxygen-containing hydrocarbon as a raw material.
2. Description of the Related Art
A conventional apparatus for producing hydrogen with the use of a hydrogen separation type reformer is proposed, for example, in Japanese Unexamined Patent Publication No. 4-325402. Disclosed in this proposal is an apparatus for producing hydrogen for a fuel cell with the use of a hydrogen separation type reformer from which hydrogen is withdrawn by a pressure reducing means. The concept of constitution of this apparatus is illustrated in FIG. 9.
As shown in FIG. 9, a hydrogen separation membrane 02 and a catalyst 08 are provided in a hydrogen separation type reformer 01. A gas as a raw material (hereinafter referred to as a raw material gas) 06 and steam 07 are fed to the hydrogen separation type reformer 01, where a reforming reaction takes place. Hydrogen formed by the reforming reaction is separated by the separation membrane 02. On a hydrogen permeation side 03 where the separated hydrogen permeates, a pressure reducing device 04 is provided to recover high purity hydrogen 05.
With the hydrogen separation type reformer 01, the raw material gas 06 comprising a hydrocarbon or an oxygen-containing hydrocarbon such as methane or methanol is introduced, and reformed on the catalyst 08 by a steam reforming reaction and a CO shift reaction to form hydrogen and carbon dioxide mainly. The hydrogen is selectively separated, for recovery, by the hydrogen separation membrane 02 built into the catalyst 08. As the hydrogen separation membrane 02, a non-porous thin film with a thickness as small as about several to 50 xcexcm, which comprises a hydrogen-permeable metal film of Pd or Pd alloy, is used, as shown in Japanese Unexamined Patent Publication No. 6-321503. As the catalyst 08, a catalyst containing a group VIII metal (Fe, Co, Ni, Ru, Rh, Pd or Pt) is preferred, and a catalyst bearing Ni, Ru or Rh or an Nio-containing catalyst is particularly preferred.
A perspective sectional view of the structure of a typical hydrogen separation type reformer is shown in FIG. 7, and a cross sectional view of the structure is shown in FIG. 8. As shown in these drawings, a hydrogen separation type reformer 10 has an outer cylinder 14 with a closed bottom 12, and an intermediate cylinder 16 and an inner cylinder 18 disposed in this order inwardly of the outer cylinder 14. The outer cylinder 14, the intermediate cylinder 16, and the inner cylinder 18 are formed upright. At an upper part of a second annular space portion 26 between the intermediate cylinder 16 and the inner cylinder 18, a preliminary reforming portion 25 is provided. Below the preliminary reforming portion 25, a plurality of hydrogen permeable pipes 34 having a metal film selectively permeable to hydrogen are disposed concentrically with the second annular space portion 26.
A burner 46 burns a fuel gas, which has been introduced through a fuel gas pipe 48, with air taken in through an air intake pipe 50 to supply thermal energy necessary for a steam reforming reaction to the second annular space portion 26 filled with a reforming catalyst A, thereby keeping the catalyst at a predetermined temperature. The fuel gas passes through an inner tube hollow portion 22, a space between the bottom 12 of the outer cylinder 14 and an annular bottom portion 24, and a first annular space portion 20, and goes outside through a combustion gas outlet 52. During this motion, the fuel gas heats a layer of the catalyst filled into the second annular space portion 26.
A process feed gas comprising a gas mixture of steam and a raw material gas composed of a hydrocarbon or an oxygen-containing hydrocarbon, such as methane or methanol, is introduced through a feed gas inlet 54 provided at an upper part of the second annular space portion 26. The process feed gas is partially converted into hydrogen at the preliminary reforming portion 25, and flowed into the layer of the catalyst filled into the second annular space portion 26, whereby the process feed gas is converted into hydrogen at a high temperature. The resulting hydrogen is selectively separated and collected by the hydrogen permeable pipes 34, passed through a third space portion 33 and flowed out through a hydrogen outlet 56 provided above the third space portion 33. The unreacted raw material gas and the resulting CO and CO2 gases, which have passed through the catalyst layer, flow through an off-gas pipe 60 having an opening at a lower part of the second annular space portion 26, and flow out of the system through an off-gas outlet 62.
With the foregoing conventional apparatus, the resulting hydrogen is withdrawn from the hydrogen separation type reformer 10 by a pressure reducing device. As is well known, a hydrogen separation membrane gives a necessary amount of hydrogen with high efficiency, accordingly, with a small membrane area, if the pressure of the hydrogen permeation side is minimized. Thus, a highly efficient pressure reducing device has been required. A vacuum pump or the like is conceivable as a pressure reducing device. However, such a rotary device has difficulty in efficiently delivering a light gas, such as hydrogen, thus requiring a high power. Furthermore, the aforementioned Japanese Unexamined Patent Publication No. 4-325402 does not propose a concrete apparatus layout including a pressure reducing device, and cannot actualize a feasible apparatus.
The present invention has been accomplished in light of these circumstances. It is an object of this invention to actualize such a concrete and feasible apparatus layout involving a pressure reducing device and provide an apparatus for producing hydrogen with the use a hydrogen separation type reformer, the apparatus having a minimal area required, and having improved durability while using a pressure reducing device.
A first aspect of the present invention, as a means of attaining the above object, is an apparatus for producing hydrogen by a steam reforming reaction, on a catalyst, of a hydrocarbon or an oxygen-containing hydrocarbon as a raw material, the apparatus comprising a hydrogen separation type reformer which has a means for heating the catalyst and which has a hydrogen separation membrane built into a layer of the catalyst for selectively separating hydrogen, a cooling means for cooling high temperature high purity hydrogen obtained from the reformer, and a hydrogen charge/discharge means disposed downstream from the cooling means and composed of a hydrogen storage material.
According to the first aspect of the invention, the following actions and effects are exhibited:
The high temperature high purity hydrogen that has been separated from the reformer is once cooled by the cooler, the indirect heat exchanger, to a temperature at which hydrogen is easily charged into the hydrogen storage material. Then, the cooled hydrogen is fed to the hydrogen storage material. As a result, the hydrogen charging rate and the amount of hydrogen charged are increased, and hydrogen can be withdrawn from the reformer at a lower pressure than the atmospheric pressure. Thus, the membrane area of the hydrogen separation can be decreased. Moreover, a required power can be decreased markedly in comparison with the power required for the use of a vacuum pump.
When hydrogen charged in the hydrogen storage material is to be delivered, the temperature of the hydrogen storage material is set at an appropriate level, whereby high pressure hydrogen can be obtained. Thus, a hydrogen compression power necessary when a compressor is used can be cut down markedly.
A second aspect of the invention is the apparatus for producing hydrogen as the first aspect of the invention, wherein the cooling means for cooling the high temperature high purity hydrogen comprises an indirect heat exchanger.
According to the second aspect of the invention, the sensible heat of the high temperature high purity hydrogen can be utilized for heating of the raw material gas and steam. Thus, the energy efficiency of the apparatus can be increased.
A third aspect of the invention is the apparatus for producing hydrogen as the first or second aspect of the invention, wherein a fluid for cooling the high temperature high purity hydrogen via the indirect heat exchanger is one or both of a raw material gas and combustion air to be fed to the hydrogen separation type reformer. As the raw material gas, a mixture of a hydrocarbon or an oxygen-containing hydrocarbon can be named.
According to the third aspect of the invention, it becomes unnecessary to use cooling water, separately, for heat exchange. Also, preheating increases the reforming efficiency, and can improve the thermal efficiency of the entire apparatus.
A fourth aspect of the invention is the apparatus for producing hydrogen as any one of the first to third aspects of the invention, wherein a fluid for cooling the high temperature high purity hydrogen via the indirect heat exchanger is one or both of air or cooling water.
According to the fourth aspect of the invention, the sensible heat of the high temperature high purity hydrogen can be recovered and utilized.
An A fifth aspect of the invention is the apparatus for producing hydrogen as any one of the first to fourth aspects of the invention, wherein the hydrogen charge/discharge means composed of the hydrogen storage material comprises at least two members of a hydrogen storing allay incorporating a heating/cooling means.
According to the fifth aspect of the invention, efficient occlusion of hydrogen can be performed.
A sixth aspect of the invention is the apparatus for producing hydrogen as the fifth aspect of the invention, wherein a fluid for cooling the high temperature high purity hydrogen via the indirect heat exchanger is cooling water, and hot water heated by heat exchange performed by the heat exchanger is used for heating of a hydrogen discharge means in the hydrogen charge/discharge means composed of the hydrogen storage material.
According to the sixth aspect of the invention, cooling water used to cool high temperature high purity hydrogen is utilized for heating the hydrogen storage material. Thus, effective use of heat can be achieved.
A seventh aspect of the invention is the apparatus for producing hydrogen as any one of the first to sixth aspects of the invention, wherein a pressure regulating means is interposed between the cooling means for cooling the high temperature high purity hydrogen and the hydrogen charge/discharge means disposed downstream from the cooling means and composed of the hydrogen storage material, to regulate the pressure of the high purity hydrogen to be fed to the hydrogen charge/discharge means.
According to the seventh aspect of the invention, the pressure regulator is installed between the hydrogen storage material and the cooling means. This prevents a rapid decrease in pressure on the hydrogen permeation side of the hydrogen separation membrane, thus improving the durability of the hydrogen separation membrane. Moreover, a rapid rise in the temperature of the hydrogen storage material associated with its hydrogen charge can also be prevented. Thermal shock to the hydrogen storage material can be lessened. Furthermore, changes over time in the amount of hydrogen production from the apparatus for producing hydrogen can be minimized and leveled off.